(a) Technical Field
The present invention relates to a method and system for controlling braking of a vehicle. More particularly, the present invention relates to a method and system for controlling braking of a vehicle, which stores regenerative braking energy in an eco-friendly vehicle equipped with an electric wedge brake on a driving wheel which receives power from a driving motor.
(b) Background Art
Generally, vehicles driven using an electric motor, i.e., eco-friendly vehicles such as pure Electric Vehicles (EV), Hybrid Electric Vehicles (HEV), and Fuel Cell Electric Vehicles (FCEV), perform regenerative braking upon braking of vehicles.
Regenerative braking systems of eco-friendly vehicles improve the fuel efficiency by converting kinetic energy of a vehicle into electric energy during braking of a vehicle, storing the electric energy in a battery, and recycling the electric energy to drive an electric motor when a vehicle drives.
In vehicles in which the regenerative braking is performed, a generative braking cooperative control technology is needed to allow the sum of a regenerative braking torque generated in an electric motor (e.g., driving motor) and a frictional braking torque generated in a brake to comply with a driver request braking torque.
In particular, an electric braking force by generative operation and rotation resistance of a motor, i.e., a regenerative braking force and a frictional braking force by a frictional braking device must be distributed. For this, cooperative control between controllers must be performed.
FIG. 1 shows an exemplary view illustrating distribution of a frictional braking torque and a regenerative braking torque to comply with a driver request braking torque. When a driver engages a brake pedal, the driver request deceleration D is determined using information such as a braking input value (e.g., detection value of brake pedal sensor) and a wheel speed based on the driver pedal operation, and the regenerative braking torque and the frictional braking torque are determined from the driver request deceleration D to comply with the driver request braking torque.
In other words, the regenerative braking torque and the frictional braking torque are distributed to comply with the driver request braking torque as shown in FIG. 1 (e.g., a target torque for control is distributed and determined), and regenerative braking control and the brake control are performed to generate distributed torques.
Moreover, to improve the regenerative braking cooperative control performance of a regenerative braking system, an Electro-Mechanical Brake (EMB) that enables individual control of the frictional braking torques of each wheel and is known to exhibit increased control performance.
The EMB is a brake that generates a braking force using an electric motor as a power source. Since the EMB does not use the hydraulic pressure to generate the braking force, the configuration is less complex than the configuration of a hydraulic brake. In addition, the EMB may improve the response and performance of various electronic control systems such as Anti Brake Systems (ABS) and the Unified Chassis Control (UCC). In the EMB, an operation of pressurizing a frictional pad to cause the frictional pad to rub with the disc is performed. In particular, the EMB receives a driver braking intention through the brake pedal, and controls the braking force of the wheel by controlling the motor driving.
An Electronic Wedge Brake (EWB) as an example of the EMB uses regenerative energy from a wedge assembly that is operated by an actuator upon braking. The EWB may implement a greater braking force than when a motor is used. As the wedge is moved by the driving of the actuator to pressurize the frictional pad, the action of the wedge may operate as an additional input of a frictional force between the frictional pad and the disc, generating a greater braking force.
FIG. 2 shows an exemplary view illustrating an electronic wedge brake 5 applied to a front wheel (e.g., driving wheel) to generate a substantially large braking torque and a typical electronic brake (wedge not used) 6 applied to a rear wheel (e.g., coupled driving wheel). Under cooperative control of a brake controller 1 and a motor controller 2, braking is performed on a vehicle by a regenerative braking force of a driving motor 3 and a frictional braking force of electronic brakes 5 and 6 mounted on the front/rear wheels while generated power of the driving motor 3 is stored in a battery 4.
The above regenerative braking system has the following limitations.
When vehicle braking starts based on the driver brake pedal input, the vehicle braking passes through a transition section, as shown in FIG. 1, during a low-speed section before the vehicle stop, and enters a state where the vehicle is stopped only by frictional braking without regenerative braking.
During the transition section in a general regenerative braking logic upon braking, the regenerative braking torque is gradually reduced, and the frictional braking torque increases as much as the regenerative braking torque is reduced. After the transition section, the regenerative braking is stopped, and only the frictional braking force is generated until a vehicle is completely stopped. In particular, the regenerative braking torque starts to decrease in the lowest vehicle speed section to store a maximum amount of regenerative braking energy in the battery.
When the response of the brake is slow, i.e., the frictional braking torque increases at a substantially slow speed and requires a substantially long transition duration, the time point to begin reducing the regenerative braking torque is advanced despite the regenerative braking being possible. Accordingly, the amount of regenerative braking energy that is recovered is reduced (see line A of FIG. 1).
On the other hand, when the response of the brake is increased, i.e., the frictional braking torque can quickly increase during the short transition duration, the time point to being reducing the regenerative braking torque can be delayed, and thus much more regenerative braking energy can be obtained. Accordingly, fuel efficiency may improve (e.g., the recovery amount and storage amount of regenerative braking energy increase) (see line B of FIG. 1).
However, since the EWB uses the regenerative energy phenomenon, a small output of the actuator can generate a large braking force, but in the low-speed section, the regenerative energy is reduced, leading to a limitation in increasing the frictional braking torque.
Accordingly, when the driver request is difficult to comply with, frictional braking torque during the transition section (e.g., fail to satisfy the driver request frictional braking torque) may occur, the frictional braking torque may not be quickly increased due to the reduction of the regenerative energy, causing disadvantages in terms of the storage of the regenerative braking energy and the fuel efficiency.
The above information disclosed in this section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.